Electro-active lenses may comprise intraocular lenses (IOL) or contact lenses that include electronic components to control a portion of the lens's refractive power, prismatic power or tinting. Intraocular lenses (IOLs), for example, may be implanted in patients' eyes either to replace a patient's crystalline lens or to complement the patient's crystalline lens. In most cases, an IOL implanted during cataract surgery is a monofocal lens, typically set for distance vision. IOLs may also include multifocal lenses, which provide both distance vision as well as focus or near distances. Accommodating IOLs capable of changing focus based on muscular movement have also been proposed. However, conventional multifocal lenses and accommodating lenses do not operate as well as a natural crystalline lens.
Automatically-focusing electronic IOL and contact lenses have been proposed, but present technical challenges. One challenge concerns the mechanism for initiating accommodation. Convergence sensing is one possible approach for addressing this. According to the principle of convergence, when a patient focuses on a specific target, the lines of sight from the two eyes intersect at that target, and the angle between the two lines of sight is essentially inversely proportional to the distance from the patient to the object. Thus, sensors may be used to determine the correct focus point for that lens, i.e., the distance from the patient to the object of regard. Providing such sensors presents its own challenges, however.
Some have advocated convergence sensing via a magnetic field using internal magnets implanted in each IOL to establish orientation relative to the an external magnetic field (i.e., terrestrial magnetic field), and then to communicate the independent orientation back and forth between the two lenses to calculate the relative angle between lenses. Among other drawbacks, this approach incurs a large electrical power demand, which is difficult to provide in a limited volume implant. In addition, for certain head orientations this approach may not work, and implanting a magnet may not be practical due. While some have proposed additionally incorporating an accelerometer to address this issue, that solution results in complex, relatively large, implementation that shares many of the flaws in the magnet-based system.
Accordingly, improved methods, systems, and components for determining a correct focus point for an electro-lens system are needed.